1. Field
One or more example embodiments relate to a light-sensing apparatus, a method of driving the light-sensing apparatus, and/or an optical touch screen apparatus including the light-sensing apparatus.
2. Description of the Related Art
Touch screen devices are devices which directly receive input data through a screen by recognizing a position of, for example, a finger, a stylus, or the like, touching the screen and performing a particular process with software. To this end, a touch screen device is equipped with a touch panel to perform such a function. Touch panels included in the touch screen devices may include resistive overlay type touch panels, capacitive overlay type touch panels, surface acoustic wave (SAW) type touch panels, infrared beam type touch panels, piezoelectric type touch panels, or the like. The touch screen device is widely used in a variety of fields as an input device for replacing a keyboard or a mouse.
A touch screen device that has been widely used employs a method of directly touching a screen of a display device with a finger or a stylus. However, as the size of a display device increases, the distance between the display device and a user increases. In this case, use of the direct touch method may be difficult to adopt. Accordingly, optical touch screen devices that may perform the same function as the existing touch screens by sensing light instead of sensing contact of a finger or a stylus have been proposed. An optical touch screen device is expected to facilitate communication not only between a user and a terminal but also between users.
In order to realize an optical touch panel, a relatively small-sized light-sensing device for sensing light is required. An amorphous silicon thin film transistor (a-Si TFT) is one of generally used light-sensing devices. However, an a-Si TFT does not exhibit a sufficient current change according to light. Accordingly, when light is incident, electric charges generated in a photodiode are accumulated in a capacitor for a defined period of time and then a signal related to light intensity is generated from the quantity of electric charges accumulated in the capacitor. When a capacitor is used as described above, a sensing time may be delayed by as long as the time for accumulating electric charges in the capacitor. In addition, a larger-sized optical touch screen device may lead to a higher parasitic capacitance.